In the fields of medical instruments, micromachinery, etc., need for miniature and lightweight actuators increases. Further, also in the fields of industrial robots, personal robots, etc., need for lightweight and flexible actuators increases.
It is said that since when an actuator is miniaturized, friction and viscosity become dominant than inertial force, a mechanism to convert energy into motion utilizing inertial force, as in motors and engines, is hard to use as an actuator for microminiature machines. As kinds of microminiature actuators in view of actuation mechanisms so far proposed, an electrostatic attractive force-type one, a piezoelectric one, an ultrasonic one, a shape memory alloy-type one, etc. are known. An electrostatic attractive force-type actuator is one wherein a plate or rod as one of the electrodes is attracted to the counter electrode, and one wherein one of the electrodes is bent by applying a voltage of the order of 100 V between the electrode and the other counter electrode scores of μm apart from the former electrode is known. A piezoelectric actuator is one wherein a voltage of hundreds to thousands is applied to the piezoelectric element made of a ceramic such as barium titanate or lead zirconate titanate to make the device expand and contract, and one capable of controlling a displacement of the order of nm is known. As an ultrasonic actuator, one to operate by causing dislocation with a combination of ultrasonic oscillation generated by a piezoelectric element or the like and frictional force is known. A shape memory alloy-type actuator largely changes in shape in accordance with temperature, and operates by changing temperature. However, these types of actuators have problems that since they are made of inorganic substance(s) such as metal(s) or ceramic(s), there is a limitation in softening and/or lightening thereof; and since they are complicated in structure, their miniaturization is not always easy; and so on.
As an actuator capable of overcoming the above problems, polymer actuators draw attention recently. For example, polymer actuators utilizing change in the shape of the hydrated polymer gel due to stimulation such as temperature change, pH change or application of electric field are devised (e.g., refer to JP-A-63-309252). However, since the change in shape of hydrated polymer gels due to various stimulations is generally very slow, and, further, the mechanical strength of hydrated polymer gels is low due to their not uniform crosslinkage structure, further improvement is necessary for actually utilizing such a polymer actuator as an actuator.
In order to overcome the above problems, a polymer actuator is devised which is composed of an ion exchange resin membrane and electrodes jointed to both surfaces thereof, and wherein an electric field is applied to the ion exchange resin membrane to bend and deform the membrane (e.g., refer to JP-B-1966645).
However, in the above-mentioned polymer actuators, an ion exchange resin containing fluorine atoms such as a sulfonic acid groups-containing fluororesin membrane (e.g., Nafion made by DuPont Co.) is often used, but there are problems that it has a large bad influence on the environment and the costs of the ion exchange resin or the membrane made of the resin are high. In the above JP-B-1966645, as an example not containing fluorine atoms, a polymer actuator using a polystyrenesulfonic acid membrane is exemplified, but there are problems that its size is very small, its shape is limited because the polystyrenesulfonic acid membrane is in a crosslinked state, and, further, its dynamic strength is poor due to its not uniform crosslinkage structure.